In general, at a transmitting side of a wireless communication system, a digital to analog converter (DAC) apparatus is provided, and as a result, a function to convert a digital signal into an analog signal is performed. As such, when the digital signal is converted into the analog signal, since the DAC does not perform sampling with an ideal impulse signal but performs sampling in a sample and hold scheme, an amplitude of a frequency response is not flat and drops like a sync waveform as illustrated in FIG. 1.
In this case, like {circle around (1)} and {circle around (2)} of FIG. 1, in the case of a narrow-band signal having a relatively small bandwidth, attenuation does not frequently occur in a whole frequency band interval, but like {circle around (3)}, attenuation of several dB occurs in a wide-band signal having a large bandwidth.
As a result, a system in which a wide-band multi-IF signal is transmitted has a frequency response characteristic, in which when respective IF signals are sampled through the DAC, as the frequency becomes high, the amplitude of the signal is further attenuated.